London Region Completes Condition Assessment on Twinned Section of Major 47 Kilometer Transmission Main
To supply roughly 500,000 people from eight different municipalities with treated water, the Lake Huron Primary Water Supply System (LHPWSS) operates a major 1200-mm (48-inch) Prestressed Concrete Cylinder Pipe (PCCP) transmission main that spans 47 kilometers (29 miles).
Pure's staff extract the PipeDiver® tool from LHPWSS's Pipeline B.
After four failures on ‘Pipeline A’ in 2012, 2010, 1988 and 1983, LHPWSS began taking a proactive approach in managing its most critical pipeline through a technology-driven management program. This includes regular inspection of the transmission main to identify specific pipe sections that have distress and are at risk of failure.
In addition to proactively managing its infrastructure, LHPWSS is also twinning the transmission main to provide redundancy in the event that Pipeline A needs to be shut down.
After a full inspection of Pipeline A in November 2012, LHPWSS assessed 6.5 kilometers (4 miles) of PCCP along the twinned ‘Pipeline B’ in December 2013 using the PipeDiver® platform. Pipeline B currently spans 28.5 kilometers (17.7 miles) and features both PCCP and Steel pipe.
The PipeDiver tool is an electromagnetic (EM) platform that operates while a pipeline remains in service. EM inspections of PCCP pipelines identify the quantity and location of broken wire wraps, which are the main structural component in PCCP. As these wraps begin to deteriorate and break, the pipe section becomes weaker and more likely to fail catastrophically.
LHPWSS’s inspection of Pipeline B was also the first use of video on the PipeDiver platform. Through the video application, LHPWSS was able to see inside the pipe under live operating conditions. The use of video during inspection provides additional information to use in conjunction with the electromagnetic data.
While the full results of the Pipeline B inspection are not finalized, the inspection demonstrates LHPWSS’s commitment to preventing transmission main failures and providing reliable water service.
This approach has been effective for LHPWSS in the past, as the 2012 inspection of Pipeline A identified only 58 pipe sections with EM anomalies out of a possible 10,000 pipe sections. This represents a distress rate of only 0.6 percent – well below industry average. Of the identified anomalies, only seven pipe sections had a relatively high level of distress.
Of the pipes with relatively high distress, two were located within a twinned section and therefore had a lower consequence of failure. The remaining five pipes were located within 3.5 kilometers (2 miles) of each other and are in the same vicinity of failures that occurred in 2010 and 2012.
LHPWSS has since verified and replaced the three most distressed pipes from the five that didn't have redundancy to mitigate the risk of another failure. Plans to replace the remaining two pipes are scheduled for 2014.
By identifying isolated problems on its major transmission main, LHPWSS is able to avoid completing expensive and challenging replacement projects while maintaining safe pipeline operation. This approach allows capital to be deferred to other projects and prevents the replacement of pipe sections with remaining useful life.